Coaxial output line for a magnetron



W. FRUTIGER COAXIAL OUTPUT LINE FOR A MAGNE'TRON Aug. 1, 1967 2Sheets-Sheet 1 Filed Dec. 26, 1963 AGENT W. FRUTIGER Aug. 1, 1967COAXIAL OUTPUT LINE FOR A MAGNETRO-N 2 Sheets-Sheet Q Filed Dec. 26,1963 llllul [FIG/'2' R E mm T NU ER F m M M L. .L W

United States Patent 3,334,266 COAXlAlL OUTPUT LINE FOR A MAGNETRONWilliam Frutiger, Liberty, Pa., assignor, by mesne assignments, toLitton Industries, inc, Beverly Hills, Calif a corporation of DelawareFiled Dec. 26, 1963, Ser. No. 333,456 6 Claims. (Cl. 315-39.53)

This invention relates to magnetrons. More particularly, it is concernedwith coupling arrangements for extracting energy from magnetrons.

Various arrangements have been employed for extracting electrical energyfrom multi-cavity magnetrons of well-known type. In one form of outputan opening in the back wall of one of the resonant cavities of themagnetron anode provides a quarter wave transformer for coupling energyfrom the cavity into an output waveguide-Another form of output couplingconsists of a coaxial arrangement including an inner conductorterminating in a coupling loop within the magnetron enclosure andadapted to extract a portion of the energy stored in the anode. Theouter conductor may be connected to the walls forming the magnetronenclosure and the inner conductor may be connected to one of the anodesegments which form the resonant cavities of the magnetron anode. Theinner conductor passes to the exterior of the magnetron enclosure andmay be arranged so as to radiate energy into a waveguide therebyexciting the waveguide. Alternatively, the inner conductor and outerconductor may be adapted to provide a coaxial output connection adaptedto be connected to a coaxial transmission line. Although the quarterwave transformer type of output is most widely used in magnetrons forcoupling to waveguide, the loop type must generally be employed when itis desired to transmit the output signal along a coaxial transmissionline.

It has proven difficult to obtain efiicient coupling of electricalenergy from the resonant cavities of the anode structure to the coaxialtransmission line by way of known forms of output coupling loops. Inorder to obtain proper coupling from the anode the coupling loop must beprecisely located and its terminal connection to an anode segmentaccurately made. The necessary degree of precision is difficult toobtain in the fabrication of any one device and is exceptionallydifficult to obtain consistently from device to device under-normalmanufacturing conditions. In addition, size and space limitations areimposed on the coupling by the physical configuration of high frequencymagnetrons. Compromises are consequently made in the spatialrelationships between the coaxial elements and the dielectric materialsemployed resulting in mismatching of impedances within the coupling.These problems lead to excessive attenuation of power and excessivereflection of energy back into the magnetron cavities as well as lack ofuniformity of coupling from device to device.

It is an object of the present invention, therefore, to provide animproved coupling arrangement for extracting energy from a magnetron.

It is also an object of the invention to provide a multicavity magnetronhaving an improved coaxial output coupling arrangement.

Briefly, a magnetron in accordance with the foregoing objects of theinvention comprises a sealed evacuated enclosure containing a meta-lanode structure having a central opening within which is supported thecathode of the magnetron. A plurality of cavity resonators are formed inthe anode structure surrounding the central cathode opening. Anauxiliary resonant cavity in the anode structure is coupled to one ofthe plurality of resonators surrounding the central opening. A coaxialoutput coupler having an inner conductor and a concentric outerconductor is sealed through the walls of the enclosure to ice providecoaxial connections externally of the enclosure. The inner and outerconductors of the coupler are connected to the anode structure atopposite sides of the auxiliary resonant cavity so as to extract aportion of the energy in the auxiliary cavity.

Additional objects, features, and advantages of magnetrons according tothe invention will be apparent from the following detailed discussionand the accompanying drawings wherein:

FIG. 1 is a plan view of a magnetron according to the inventionpartially in cross-section taken generally along the line 1-1 of FIG. 2,

FIG. 2 is an elevational view in cross-section taken generally along theline 22 of FIG. 1, and

FIG. 3 is an elevational view in cross-section of a portion of themagnetron of FIGS. 1 and 2 taken generally along the line 33 of FIG. 2.

A magnetron according to the invention as illustrated in the drawingsincludes a cylindrical body 10 closed by an upper end plate 11 and alower end plate 12 to form an enclosure. A ring-shaped anode block 13 ismounted to the body within the enclosure. An even numbered plurality ofradially extending segments or vanes 14 are fastened at their outeredges to the inner surface of the anode block. The inner edges or tipsof the segments terminate in spaced apart relationship adjacent thecentral region of the anode structure providing space for an electronemissive cathode 15. The space between each pair of segments constitutesan open ended resonant cavity.

An annular conductive strap coaxial with the anode block and cathode isconnected to the upper ends (as viewed in FIG. 2) of alternate segmentsadjacent their inner edges. The segments between the alternate connectedsegments are notched so that they are not contacted by the strap. Asimilar strap 21 is connected to the lower ends of those anode segmentsnot contacted by the upper strap, and the segments contacted by theupper strap are notched at their lower ends so as not to contact thelower strap. As is well known in the magnetron art, the straps connectalternate segments together in order to restrict the magnetron tooperation in only the predominant or 11' mode and suppress other modesof oscillation.

An upper magnet pole piece 22 is mounted on the upper end plate 11between the upper ends of the anode segments and the upper plate. Alower magnet pole piece 23 is similarly mounted on the lower end plate12. A cylindrical magnet 24 encircles the body of the magnetron. Themagnet is held in place by retaining members 25 and 26. Magnetic fluxflows from the magnet through the retaining members, end plates, andmagnet pole pieces to create a magnetic field in the interaction spacecentrally of the anode.

The cathode 15 passes through a central bore (not shown) in the lowermagnet pole piece 23, and is positioned centrally of a bore 27 in theupper magnet pole piece 22. The cathode structure is suitable sealed tothe lower end plate in insulating relationship to provide a hermeticseal and permit the cathode leads 28 to be available externally of themagnetron enclosure.

As illustrated in the drawings an auxiliary resonant cavity 30 isprovided in the anode block 13. A slot 31 in the anode 'block extendsradially of the anode structure and opens into one of the resonantcavities defined by the segments centrally of the back wall of thecavity. The end of the slot farthest removed from the center of theanode is terminated in a hole 32. The hole and slot in the anode blockprovide a series resonant circuit. The dimensions of the hole and slotare such that the auxiliary cavity is resonant at the same frequency asthe resonant cavities.

Electrical energy is transmitted from the anode to the a exterior of themagnetron enclosure by a coaxial output coupler 40 (indicated in phantomin FIG. 1). The coupler includes a hollow cylindrical outer conductor 41which is sealed through an opening in the upper end plate by means of anadapter 42. The outer conductor 41 extends within the enclosure parallelto the central axis of the magnetron toward the anode block 13. A hollowcylinder of insulating material 43, for example a high alumina ceramic,metallized along the upper portion of its outer periphery is sealed tothe inner periphery of the outer conductor. The ceramic cylinder extendsinto the enclosure toward the anode beyond the outer conductor.

The inner conductor 44 of the coupler consisting of a cylindrical rod islocated centrally of the hollow ceramic cylinder and is spaced from theinner walls of the cylinder. A conductive end cap or cup 45 is sealed tothe inner conductor and to the metallized end of the ceramic cylinderthereby providing a completely sealed enclosure. The

end cap 45 and the outer conductor 41 are spaced from each other asufficient distance so that the impedance characteristics of the coaxialcoupler are not affected by that spacing but are primarily determined bythe dielect-ric nature of the ceramic cylinder and air space interveningbetween the inner and Outer conductor. Proper spacing between the endcap and outer conductor provides a slight capacitance which balances theinductance of the lower portion of the inner conductor thus helping torender the coupler non-reactive.

The inner conductor 44 of the coaxial coupler is connected to the anodeblock adjacent one side of the slot 31 of the auxiliary resonant cavity.A conductive tab 46 is attached to the outer conductor, and acylindrical lead 47 is connected between the tab and the anode block.The lead is connected to the anode block adjacent the slot and directlyopposite the slot from the inner -conductor. These connections to theanode block are precisely made at the proper location by virtue ofmounting holes in the block adapted to receive the inner conductor andthe outer conductor lead.

A coaxial output connector 50 of known type is mounted on the exteriorof the enclosure. The inner and outer conductors 51 and 52 of theconnector are suitably connected to the inner and outer conductors 44and 41 of the coupler to provide proper matching of impedances.

The connector is adapted to be connected with a mating connector of acoaxial transmission line.

The magnetron according to the invention operates in the usual manner ofknown open ended multi-cavity magnetrons to produce electricaloscillations. In the magnetron illustrated electrical energy isextracted from the anode structure and transmitted to the exterior ofthe enclosure by the auxiliary resonant cavity 30 and the coaxial outputcoupler 40. Energy passes into the auxiliary cavity by way of theopening between the auxiliary cavity and one of the plurality ofcavities provided by the anode segments. The auxiliary resonant cavity30 is constructed so as to resonate at the frequency of oscillationsproduced in the other cavities of the magnetron. Therefore, the voltageson the regions of the block on opposite sides of the slot are 180 out ofphase. The inner conductor 44 and the lead 47 for the outer conductor ofthe coupler are connected to these regions of opposite potential andserve to extract a portion of the electrical energy circulating in theauxiliary cavity. The amount of energy extracted from the auxiliarycavity is dependent on the position of the connections to the coaxialcoupler along the length of the slot. The nearer the connections are tothe center of the anode the greater the amount of power intercepted.

In magnetrons according to the invention uniformity of coupling from theanode to the output connector is obtained. Each device is substantiallysimilar to every other device since the assembly of the structuralelements is predetermined by the configuration of the elementsthemselves and the individual elements of structure can be fabricated toclose tolerances. Coupling from the anode in the device according to theinvention depends primarily on the dimensions of the hold and slot ofthe auxiliary cavity and the location of the mounting holes for makingthe coaxial output coupler connections to the anode block. Thesedimensions can be very precisely controlled in the elements asmanufactured and are not subject to alteration during the assembly ofthe device. Since the assembly of the structural elements can beprecisely predetermined, it is possible consistently to obtain thedesign parameters of the output coupling arrangement.

The coaxial coupler is prefabricated as a subassembly and thenaccurately connected in position on the anode block by virtue of themounting holes in the block, thereby providing both ease and precisionin assembling to the magnetron. There is no supporting structure ofinsulating material extending from the inner conductor to the outerconductor along any portion of their length. The structure as shownprovides a ceramic cylinder in combination with an air dielectricbetween the coaxial conductors. This arrangement makes it possible toprovide a coaxial coupler which is sufficiently small to be used in highfrequency devices, which is of rugged mechanical construction, and whichalso can be designed to be of proper impedance. These various featuresmake it possible to obtain close matching of impedances between theanode structure, the coaxial coupler, and the output connector withconsequent low power attenuation, negligible reflection of electricalenergy, and increased transfer of energy to the load.

What is claimed is:

1. A magnetron comprising a sealed evacuated enclosure containing ametal anode structure having a central opening within which is supportedthe cathode of the magnetron,

a plurality of cavity resonators in said anode structure surrounding thecentral opening,

an auxiliary resonant cavity in said anode structure coupled to one ofsaid plurality of cavity resonators, and

a coaxial output coupler having an inner conductor and a concentricouter conductor,

said conductors of the coaxial output coupler being connected to saidanode structure at opposite sides of said auxiliary resonant cavity toextract a portion of the energy in said auxiliary resonant cavity.

2. A magnetron comprising a cylindrical anode block,

a plurality of segments extending radially inwardly from said block andproviding a resonant cavity between each pair thereof,

the inner tips of said segments being spaced apart and providing acircular cathode space centrally of the anode block,

an auxiliary resonant cavity in said anode block coupled to one of saidresonant cavities, and

a coaxial output coupler having an inner conductor and a concentricouter conductor,

said conductors of the coaxial output coupler being connected to saidanode block on opposite sides of said auxiliary resonant cavity toextract a portion of the energy in said auxiliary resonant cavity.

3. A magnetron comprising a sealed evacuated enclosure containing ametal anode structure having a central opening within which is supportedthe cathode of the magnetron,

a plurality of cavity resonators in said anode structure surrounding andopening into the central opening,

an auxiliary resonant cavity in said anode structure opening into one ofsaid plurality of cavity resonators, and

a coaxial output coupler having an inner conductor and a concentricouter conductor,

means connecting the inner and outer conductors of the coaxial outputcoupler to the anode structure at opposite sides of said auxiliaryresonant cavity to extract a portion of the energy in said auxiliaryresonant cavity.

4. A magnetron comprising a sealed evacuated enclosure containing acylindrical metal anode block,

a plurality of segments extending radially inwardly from said block andproviding a resonant cavity between each pair thereof,

the inner tips of said segments being spaced apart and providing acirciut cathode space centrally of the anode block,

an auxiliary cavity in said anode block extending radially outwardlyfrom one of said resonant cavities and opening into said one cavity toextract energy therefrom,

a coaxial coupler including an outer cylindrical conductor passingthrough and sealed to the walls of said enclosure and a concentric innerconductor sealed to the other conductor in insulating relationship,

means connecting the outer conductor to the anode block adjacent oneside of said auxiliary resonant cavity, and

means connecting the inner conductor to the anode block adjacent theopposite side of said auxiliary resonant cavity whereby energy isextracted from said auxiliary resonant cavity.

5. A magnetron comprising a sealed evacuated enclosure containing acylindrical metal anode block,

a plurality of segments extending radially inwardly from said block andproviding a resonant cavity between each pair thereof,

the inner tips of said segments being spaced apart and providing acircular cathode space centrally of the anode block,

a slot in said anode structure extending radially outwardly from one ofsaid plurality of cavity resonators,

a hole in said anode structure at the end of said slot removed from saidone cavity resonator,

said hole and slot providing an auxiliary cavity resonant at thefrequency of resonance of said cavity resonators,

a coaxial output coupler sealed to a Wall of said enclosure andextending to the interior and exterior of the enclosure having an innerconductor and a concentric outer conductor,

means connecting the inner conductor to the anode structure adjacent'oneside of the slot, and

means connecting the outer conductor to the anode structure adjacent theopposite side of the slot.

6. A magnetron comprising in combination a sealed evacuated enclosurecontaining a metal anode structure,

a plurality of cavity resonators in said anode structure,

a coaxial output coupler for extracting energy from one of said cavityresonators and transmitting the energy to the exterior of saidenclosure,

said output coupler comprising a conductive hollow cylindrical outerconductor sealed to a wall of said enclosure and extending to theinterior and exterior of the enclosure,

a hollow cylinder of insulating material sealed Within said outerconductor and having a portion extending beyond the outer conductor intothe interior of said enclosure toward the anode structure,

an inner conductor connected to the anode structure adjacent one side ofsaid one cavity resonator and extending to the exterior of saidenclosure concentric with and spaced from the outer conductor andcylinder of insulating material,

a sealing member sealing the inner conductor to the cylinder ofinsulating material in said portion of the cylinder extending beyond theouter conductor, and

a conductive member connected between the outer conductor and the anodestructure adjacent the side of the cavity opposite the inner conductorwhereby the outer conductive member and the inner conductor extract aportion of the energy in said one cavity resonator.

No references cited.

HERMAN KARL SAALBACH, Primary Examiner.

S. CHATMON, JR., Assistant Examiner.

1. A MAGNETRON COMPRISING A SEALED EVACUATED ENCLOSURE CONTAINING AMETAL ANODE STRUCTURE HAVING A CENTRAL OPENING WITHIN WHICH IS SUPPORTEDTHE CATHODE OF THE MAGNETRON, A PLURALITY OF CAVITY RESONATORS IN SAIDANODE STRUCTURE SURROUNDING THE CENTRAL OPENING, AN AUXILIARY RESONANTCAVITY IN SAID ANODE STRUCTURE COUPLED TO ONE OF SAID PLURALITY OFCAVITY RESONATORS, AND A COAXIAL OUTPUT COUPLER HAVING AN INNERCONDUCTOR AND A CONCENTRIC OUTER CONDUCTOR, SAID CONDUCTORS OF THECOAXIAL OUTPUT COUPLER BEING CONNECTED TO SAID ANODE STRUCTURE ATOPPOSITE SIDES OF SAID AUXILIARY RESONANT CAVITY TO EXTRACT A PORTION OFTHE ENERGY IN SAID AUXILIARY RESONANT CAVITY.